I've balanced the weight in the elbows of my knees (legs are crossed and bent during the exercise). Not sure if thats dangerous or not, only that it is a quick solution to the problem of no weight belt or backpack.
If you use a dumbell you can always just lift it with your feet as well. Also an easy way to make one for about 10 bucks is to get a cheap weight lifting belt and attach a chain to it. I made mine this way and I've had it for a little over 2 years and its held up great and supports up to 150 lbs.
__________________ You have a hand you have the power to create your body the way you want it.